[Pacemaker] RFC: "deadman" dependencies

[Andrew Beekhof]

On Thu, Jun 24, 2010 at 5:33 PM, Lars Marowsky-Bree <lmb at novell.com> wrote:
> Hi,
>
> this an a request for comments for so-called deadman dependencies, and
> how they should/could be implemented. I'm intentionally using the
> general user and not the dev list to get more user-feedback.
>
> The idea itself is simple: it would allow to define that resources
> depend on certain attributes, and if those attributes go away, that the
> cluster would invoke fencing, to immediately terminate the resource.
> (Instead of normal stop operations.) The goal is to significantly reduce
> recovery time here. (This is part of the ideas needed for geo
> clustering.)
>
> Theoretically, an attribute to a rsc_order might work - clearly, the
> attribute (or whatever pre-requisite) has to come first. Basically, an
> order_type="deadman" (a stronger form of "Mandatory")?
>
> What are your thoughts on the syntax?

I'd be inclined to make it a new kind of constraint, and failing that,
overload rsc_colocation rather than rsc_order.

Perhaps:

<rsc_colocation rsc="XYZ" with-attr="ABC" somename="deadman"/>

Not sure what "somename" should be.  recovery?

> Implementation-wise, unsatisfied deadman-dependencies would translate to
> the node where affected resources are active (started, promoted, failed
> stops, unmanaged non-withstanding) being scheduled for fencing
> immediately. In fact, due to the recovery time goals, I'd suggest to
> special case this - if the transition contains unsatisfied deadman
> dependencies, skip everything both the STONITH resources and fencing

s/everything both/everything except both/ ?

> requests, and postpone all other start/stop actions to further
> transitions; we don't want anything to interfere with this phase.
>
>
> Regards,
>    Lars
>
> --
> Architect Storage/HA, OPS Engineering, Novell, Inc.
> SUSE LINUX Products GmbH, GF: Markus Rex, HRB 16746 (AG Nürnberg)
> "Experience is the name everyone gives to their mistakes." -- Oscar Wilde
>
>
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